Piston Pump having an Inlet Valve

ABSTRACT

A piston pump includes a piston, a sealing element sealing the piston radially with respect to a cylinder, and an inlet valve arranged on the piston. The inlet valve includes a valve cage holding a closing member. The sealing element is integrally designed with the valve cage.

PRIOR ART

The invention relates to a piston pump comprising a piston, a sealingelement on the piston sealing radially with respect to a cylinder, andan inlet valve arranged on the piston, said inlet valve being designedwith a valve cage holding a closing member. In addition, the inventionrelates to a vehicle brake system comprising a piston pump of this type.

In known vehicle brake systems, the “hydraulic power unit” is a fixedcomponent. It is used to meter the brake pressure and, to this end, hasa pump, which is generally a piston pump, in which a piston isdisplaceable in a cylinder. The piston is displaced in a two-cycleoperation. In a first cycle, a fluid to be conveyed, for example brakefluid, is sucked up through an inlet valve. In a second cycle, the fluidis discharged through an outlet valve. The piston is sealed with respectto the inner surface of the cylinder by means of a sealing element andis also guided in the cylinder during its stroke movement by saidsealing element. A piston pump of this type is known for example from DE10 2005 017 131 A1.

The object of the invention is to create a vehicle brake systemcomprising a piston pump, in which the seal between the piston and thecylinder is designed so as to be permanently reliable whilst, at thesame time, creating an arrangement which is particularly cost-effectiveon the whole.

DISCLOSURE OF THE INVENTION

In accordance with the invention, a piston pump comprising a piston, asealing element sealing the piston radially with respect to a cylinder,and an inlet valve arranged on the piston is created, said inlet valvebeing designed with a valve cage holding a closing member. The sealingelement and the valve cage are designed in one piece.

With the solution according to the invention, the one-piece componentformed from the sealing element and valve cage of the inlet valve can beproduced in a more cost-effective manner compared to two individualcomponents. In addition however, the solution according to the inventionaffords further surprising advantages. In particular, the assembly ofthe sealing element is also simplified considerably with this solution,because the sealing element is additionally stabilized in terms of shapeby means of the valve cage. In addition, the valve cage can be used inan automatic assembly device as a position recognition means for thesealing element. Lastly, the one-piece component can be heldparticularly easily on the respective piston by a respective returnspring and can thus be fastened to said piston in a very simple andcost-effective manner. This will be explained in greater detailhereinafter as a development of the solution according to the invention.

In accordance with a first advantageous development of the piston pumpaccording to the invention, the sealing element and the valve cage areproduced from plastic.

Due to the selective choice of a plastic which is sufficientlydimensionally stable for the valve cage and also sufficiently resilientfor the sealing element, it is possible to produce the one-piececomponent according to the invention in only a single manufacturingprocess.

In accordance with a second advantageous development of the piston pumpaccording to the invention, a spring support for a return springsupporting the piston relative to the cylinder is formed on the sealingelement.

The spring support designed in such a way enables a particularlyspace-saving arrangement of the return spring, wherein said returnspring may, at the same time, be selected to be particularly long andlarge in diameter. The return spring can therefore develop highrestoring forces with a small installation space.

In accordance with a third advantageous development of the piston pumpaccording to the invention, the sealing element has a sealing lipresting against the cylinder, said sealing lip ending in an axiallyset-back manner relative to the spring support on the side facing awayfrom the return spring.

The spring support axially set back in such a way compared to theeffective surface of the return spring prevents the respective sealinglip from being damaged due to the applied return spring and therestoring forces thereof.

In accordance with a fourth advantageous development of the piston pumpaccording to the invention, the sealing element is designed with anaxial groove, which is open towards the high-pressure area of thepiston/cylinder arrangement.

During operation of the piston pump, in the axial groove open in such away towards the high-pressure area of the piston/cylinder arrangement,the pressure prevailing in the high-pressure area may infiltrate theaxial groove and thus expand it. At the same time, the radially outerpart of the sealing element, that is to say the part which lies radiallyoutwardly beside the axial groove, is then pressed against the adjacentinner wall of the cylinder. With increasing pressure in thehigh-pressure area, a reinforcement of the support of the sealingelement against the cylinder also thus develops, and therefore animproved seal. At the same time, the leakage behavior in the piston andalso the guidance of the piston in the cylinder are improved.

In accordance with a fifth advantageous development of the piston pumpaccording to the invention, the sealing element is designed in a steppedmanner on its side facing the piston.

The stepped design of the sealing element leads to a comparatively largecontact area between the piston and the sealing element. This largecontact area improves the fastening of the sealing element. Inparticular, the sealing element can be fixed by being pressed on againstthe axially extending flanks of the step(s). At the same time, thesealing element is centered at these flanks relative to the piston. Theradially directed flanks of the step(s) are used to support the sealingelement with respect to the piston, which is particularly advantageouswhen the piston is reset by means of the above-mentioned return spring.

In accordance with a sixth advantageous development of the piston pumpaccording to the invention, the sealing element surrounds the piston.

The sealing element surrounds a portion of the piston in this manner inparticular at a step, a groove or a phase of the piston in such a waythat the sealing element hooks behind the piston in the axial directionby means of a pawl, which is peripheral or peripheral over portions. Apositive-fit connection between the piston and sealing element is thuscreated, which can be easily produced or pre-assembled, even in anautomatic manufacturing process, due to the above-mentioned slightlyresilient property of the material of the sealing element.

In accordance with a seventh advantageous development of the piston pumpaccording to the invention, the piston is designed in two parts with afirst part turned towards a drive and a second part turned towards thesealing element.

The individual parts of the piston thus designed in two parts can beassigned specific functions. The first part is thus used to transfer thethrust generated at the drive to the second part, which in turn ensuresthe flow of fluid, in particular brake fluid, into the inlet valve. Thehigh-pressure area inside the cylinder is then defined by means of thesealing element and sealed with respect to the low-pressure area. Thesecond part pushes the sealing element into the cylinder and is in turnpushed by the first part. The piston is reset starting from the returnspring by transferring the restoring thrust forces via the sealingelement and the second part onto the first part. The individual partscan be optimized in a simpler manner in view of the material selectionand possible production methods, as would be the case with a one-partpiston.

In accordance with an eighth advantageous development of the piston pumpaccording to the invention, the first part is designed as a solidcylinder and the second part is designed as a hollow cylinder.

The first part designed as a solid cylinder can be produced in a verycost-effective manner and, in particular, can transfer high thrustforces. It is advantageously produced from plastic, to which reinforcingfibers are preferably added. The second part designed as a hollowcylinder may advantageously already be formed as a blank with acylindrical hollow chamber. The second part is preferably produced frommetal and in particular is designed as a sinter cast part or as adeep-drawn part. In a part of this type, merely at least one radialopening is to be formed, through which the fluid to be sucked up canthen flow radially from the outside in, in the direction of the inletvalve during operation of the piston pump.

The above-mentioned object is furthermore also achieved by a vehiclebrake system comprising a piston pump of this type according to theinvention, wherein corresponding advantages are achieved, as alreadydescribed above for the piston pump.

An exemplary embodiment of the solution according to the invention willbe explained in greater detail hereinafter on the basis of theaccompanying schematic drawings, in which:

FIG. 1 shows a longitudinal section of a piston pump according to theprior art,

FIG. 2 shows the detail II in FIG. 1 in an enlarged scale,

FIG. 3 shows a longitudinal section of a first exemplary embodiment of apiston pump according to the invention,

FIG. 4 shows the detail IV in FIG. 3 in an enlarged scale,

FIG. 5 shows a longitudinal section of a second exemplary embodiment ofa piston pump according to the invention, and

FIG. 6 shows the detail VI in FIG. 5 in an enlarged scale.

A piston pump 10 according to the prior art is illustrated in FIGS. 1and 2 and comprises, inter alia, a piston arrangement 12, which isformed from a cylinder 14 and a piston 16 mounted displaceably therein.The piston arrangement 12 further comprises an inlet valve 18 and anoutlet valve 20. These valves 18 and 20 are provided so that, during itsstroke movement in the cylinder 14, the piston 16 can suck a fluidthrough an inlet 22 into a high-pressure chamber or high-pressure area24 inside the cylinder 14 and can discharge this fluid again, underpressure, from the high-pressure area 24 through an outlet 26. The fluidis a brake fluid in the present case.

The piston 16 is biased resiliently in the axial direction by means of areturn spring 28 located in the high-pressure area 24. On the basis ofFIG. 1, the return spring 28 is supported at its left end against theend face of the cylinder 14 and presses at its right end against aspring support 30. The spring support 30 is coupled fixedly to thepiston 16 so that the return spring 28 presses accordingly against thepiston 16 via the spring support 30.

A sealing element 32 is also arranged between the piston 16 and thecylinder 14 and seals the high-pressure area 24 in the cylinder 14. Thesealing element 32 is annular and surrounds the piston 16 at the outersurface thereof. The sealing element 32 is held fixedly on this outersurface by means of a valve cage or valve housing 34 of the inlet valve18, said valve cage or valve housing being slid over the piston 16. Atthe valve housing 34, the spring support 30 is also shaped in the formof a shoulder. The sealing element 32 retained in such a way liesradially inwardly against the inner surface of the cylinder 14, so as toslide along and seal said inner surface of the cylinder.

The valve housing 34 is designed in a beaker-shaped manner as a cage, inthe interior of which a screw-shaped return spring 36 is located andpresses against a spherical closing member 38. The closing member 38thus lies (in the operating state illustrated in FIGS. 1 and 2) againsta valve seat 40, which is formed on the end face of the piston 16. Theclosing member 38 is lifted from this valve seat 40, against the forceof the return spring 36, when the piston 16 is withdrawn to the rightfrom the cylinder 14, based on FIG. 1. With this movement, the inletvalve 18 is thus opened and fluid is sucked into the high-pressure area24.

The sealing element 32 according to FIGS. 1 and 2 has a main body 42,which is basically square in cross-section and on which a sealing lip 44facing the high-pressure area 24 is formed.

FIGS. 3 and 4 show a piston pump 10 according to the invention. Thispiston pump likewise has a piston arrangement 12 comprising a cylinder14 and a piston 16 displaceable therein. Furthermore, an inlet valve 18and an outlet valve 20 are likewise provided. The piston 16 is biasedresiliently by a return spring 28 located in a high-pressure area 24,said return spring pressing against a spring support 46 according to theinvention coupled fixedly to the piston 16.

A sealing element 48 according to the invention is also located betweenthe piston 16 and the cylinder 14, said sealing element being retainedfixedly on the piston 16 and being able to slide along the inner surfaceof the cylinder 14. This sealing element 48 is formed in one piece witha valve housing 50 according to the invention, in such a way that thespring support 46 and the sealing element 48 are also designed in onepiece. The one-piece design of the spring support 46 and sealing element48 enables an axially very short, more compact design with a smallerdead space volume. The sealing element 48 can additionally be biased bythe return spring 28. A radially very wide support surface is alsoprovided for the return spring 28 at the spring support 46.

As can be seen in FIG. 4, the sealing element 48 is designed with anaxial groove 52, which is open in the direction of the high-pressurearea 24. The pressurized fluid located in the high-pressure area 24accordingly also infiltrates this axial groove 52. The two inner,mutually opposed side faces or flanks 54 and 56 of the axial groove 52are pressed radially away from one another by this fluid. In particular,the lip-shaped part or portion 58 of the sealing element 48 locatedradially outwardly from the axial groove 52 and which can also bereferred to as a sealing lip is pressed radially outwardly and thereforeagainst the inner surface of the cylinder 14. As the pressure increasesin the high-pressure area 24, this portion 58 of the sealing element 48thus also rests more heavily against the cylinder 14, where it thusprovides an improved seal. In addition, the guidance of the piston 16 inthe cylinder 14 is improved.

FIGS. 5 and 6 illustrate an exemplary embodiment of a sealing element48, in which the end of the lip-shaped portion 58 or the sealing lip ofthe sealing element 48 is set back axially towards the side facing awayfrom the return spring 28, relative to the radially directed plane ofthe spring support 46. A distance from the return spring 28 is thus alsoproduced axially, so that the return spring 28 cannot damage thelip-shaped portion 58. The return spring 28 also presses the core of thesealing element 48 axially together, however, so that it is pressedradially outwardly.

In both exemplary embodiments shown in FIGS. 3 to 6, the piston 16 isformed in two parts from a first part 60 and a second part 62. The firstpart 60 is a solid cylindrical, rod-shaped structure, which is injectionmolded from plastic and is specifically adapted to transfer axiallydirected shear forces from an eccentric drive (not illustrated) to thesecond part 62 and thus to the sealing element 48. The second part 62 isa hollow cylindrical sinter cast part, which has a shoulder or a step 64and 66 at each of its two ends. The step 64 encompasses the first part60 radially outwardly at the end region thereof, wherein the first part60 is fixed non-positively in the interior of the step 64 by means of apress fit. The step 66 is located adjacent to the sealing element 48 andis surrounded thereby radially outwardly in the axial direction. Aportion 68 of the sealing element 48, which forms the core thereof,rests radially outwardly against the step 66 and forms a press fittherewith. A further portion 70 of the sealing element 48, which islocated radially completely outwardly, surrounds the step 66 of thesecond part 62 completely in the form of a type of arm or sleeve. Aplurality of pawls 72 is formed peripherally on this portion 70, saidpawls hooking behind the radially outer region of the step 66 and thusproducing a positive-fit connection to the second part 62 in the axialdirection.

Furthermore, an annular chamber 74 widened in the radial direction iscreated in the border area between the sealing element 48 and the valvecage or valve housing 34 thus formed in one piece. This annular chamber74 enables fluid to flow off temporarily, said fluid passing through thegap formed between the valve seat 40 and the closing member 38 when theinlet valve is opened. The annular chamber 74 receives this fluid andthus reduces the pressure surges which would otherwise occur. It thusacts in a damping manner in terms of the pressure impulses produced. Anundercut in the valve housing 34 is not necessary for the annularchamber 74, but is created merely by a stepped recess in the valvehousing 34 in cooperation with the adjacent second part 62 of the piston16, which is particularly favorable in terms of manufacture.

1. A piston pump comprising: a piston; a sealing element configured toseal the piston radially with respect to a cylinder; and an inlet valvearranged on the piston, said inlet valve including a valve cage holdinga closing member, wherein the sealing element and the valve cage are onepiece.
 2. The piston pump as claimed in claim 1, wherein the sealingelement and the valve cage are produced from plastic.
 3. The piston pumpas claimed in claim 1, wherein a spring support for a return springsupporting the piston relative to the cylinder is formed on the sealingelement.
 4. The piston pump as claimed in claim 3, wherein: the sealingelement includes a sealing lip resting against the cylinder, and saidsealing lip ends in an axially set-back manner relative to the springsupport on the side facing away from the return spring.
 5. The pistonpump as claimed in claim 1, wherein: the sealing element includes anaxial groove, and the axial groove is open towards the high-pressurearea of the piston/cylinder arrangement.
 6. The piston pump as claimedin claim 1, wherein the sealing element is configured in a steppedmanner on its side facing the piston.
 7. The piston pump as claimed inclaim 1, wherein the sealing element surrounds the piston.
 8. The pistonpump as claimed in claim 1, wherein the piston is designed in two partswith a first part turned towards a drive and a second part turnedtowards the sealing element.
 9. The piston pump as claimed in claim 8,wherein: the first part is a solid cylinder, and the second part is ahollow cylinder.
 10. A vehicle brake system comprising: a piston pumpincluding (i) a piston, (ii) a sealing element configured to seal thepiston radially with respect to a cylinder, and (iii) an inlet valvearranged on the piston, said inlet valve including a valve cage holdinga closing member, wherein the sealing element and the valve cage are onepiece.